1. Field of the Invention
This invention relates to cooling electronic enclosures and, more particularly, to the use of air movers to cool electronic enclosures.
2. Description of the Related Art
Electronic enclosures may contain many different electronic devices that are designed to operate within certain temperature ranges. However, when operating, each electronic device may generate heat. If enough heat is generated within the enclosure to cause any of the enclosed electronic devices to operate outside of their operational temperature range, problems may occur. For example, in some cases, increased temperature may cause a system to malfunction or behave erroneously. Sometimes, increased heat may even damage the electronic devices or components within the enclosure.
In order to reduce heat-related problems, many electronic enclosures include cooling devices. One simple example of a cooling device is a passive heat sink that radiates heat from a device into the surrounding air. A passive heat sink is simply a piece of metal attached to a component in such a way that the component transfers heat to the heat sink. By increasing the surface area from which heat can be radiated, heat sinks increase the amount of heat that can be transferred from a component to the surrounding air. Some heat sinks have fins, which further increase the surface area and allow even more heat to be radiated away. In some systems, passive heat sinks may be all that is needed to ensure proper cooling. For example, convection will cause heated air to rise higher than cooler air, so in some cases, hotter air will naturally be circulated away from the heat-generating component while cooler air is constantly being circulated towards the component. In other systems though, factors such as the size of the enclosure or the orientation of the device within the enclosure may limit the beneficial effects of convection. In such situations, other cooling devices may be needed to prevent heat-related problems.
One problem with systems that simply radiate heat is that the heat may accumulate inside an area in the enclosure. For example, convection may no longer assist in cooling if all of the air in an area becomes equally heated. One situation where this might arise is if a heat-generating component is located near the top of an enclosure. The top component may quickly lose any benefits of convection due to the accumulation of heated air in the top of the enclosure. Another situation where this might arise occurs when many devices are mounted in close proximity in an enclosure. Each device""s ability to radiate heat away from itself may be limited if the surrounding air has already been heated by the other components.
In order to alleviate problems that arise when heat accumulates, many systems incorporate devices that can move already-heated air away from an area and draw less-heated air into the area. Air movers such as fans and blowers (e.g., centrifugal fans) are popular cooling devices because they are capable of moving heated air away from and/or cooler air towards areas where heat-related problems may arise. By regularly moving heated air away from or cooler air over a component, the component""s ability to radiate heat is better maintained. For example, air movers may move either warmer or cooler air to another section of an enclosure, move heated air from inside an enclosure to the outside of the enclosure, or move cooler air from outside an enclosure to the inside of the enclosure. In many enclosures, several air movers may be used to move the proper volume of air necessary to reduce heat-related problems to an acceptable level. Additional air movers may also be included to provide redundancy, so that if an air mover fails, one of the redundant air movers can be used as a replacement.
Various embodiments of a method and apparatus for maintaining cooling efficiency during air mover failure are disclosed. In some embodiments, an electrical enclosure includes a heat-generating thermal load, multiple air movers configured to remove heat from the thermal load, and a backward-airflow reducing device configured to reduce the amount of air that can be drawn backwards through an air channel if an air mover fails. When functioning, each air mover is configured to draw air into an intake and to expel air from an exhaust so that the air within an air channel moves in a forward direction. The air movers remove heat from the thermal load by moving cooler air across the thermal load, allowing the thermal load to transfer heat to the air. In one embodiment, some of the air movers may be configured to blow air across the thermal load. In another embodiment, the air movers may instead draw air across the thermal load. The thermal load may, in some embodiments, comprise one or more disk drives.
The backward-airflow reducing device may be coupled to the exhaust side of the air mover in some embodiments. In other embodiments, the backward-airflow reducing device may instead be coupled to the intake side of the air mover. In still other embodiments, the backward-airflow reducing device may be coupled elsewhere within the enclosure. While the air mover is functioning, the backward-airflow reducing device may be configured to allow air to be drawn into the intake and expelled from the exhaust of the air mover.
In some embodiments, the backward-airflow reducing device may include a valve. In one embodiment, the valve may be configured to open in response to air being expelled from the exhaust when the air mover is functioning. In another embodiment, the valve may be configured to open in response to the air being drawn into the intake when the air mover is functioning. The electrical enclosure may, in one embodiment, include an electronic circuit configured to sense whether the air mover has failed and to generate a signal that causes the valve to close if the air mover has failed. In one embodiment, the valve may be configured to close in response to a drop or a reversal in air pressure that occurs when the air mover fails. In other embodiments, the valve may include a spring configured to open the valve if the air mover is functioning and/or to close the valve if the air mover is not functioning. In one embodiment, the valve may close due to gravity.
In other embodiments, a method for maintaining cooling efficiency in an electrical enclosure during air mover failure is disclosed. The method includes heating a portion of the electrical enclosure, operating multiple air movers within the enclosure to cool the heated portion of the enclosure by moving air across it, detecting whether one of the air movers has failed, and, if one of the air movers has failed, reducing the amount of air that can be drawn backwards through an air channel. In some embodiments, the enclosure may be heated by one or more disk drives. Operating the air movers may include blowing air or drawing air across the heated portion of the enclosure. A backward-airflow reducing device may reduce the amount of air that can be drawn backwards through an air channel. Detecting whether one of the air movers has failed may, in some embodiments, include passively sensing whether an air mover is functioning or not. For example, passively sensing may include responding to a drop or reversal in air pressure or responding to gravity or a combination of gravity and air pressure change or other means.
Thus, an air mover may be configured for use in an electrical enclosure. The air mover may include an intake configured to draw air into the air mover, an exhaust configured to expel air out of the air mover, and a backward-airflow reducing device configured to reduce the amount of air that can be drawn backwards through the air mover if the air mover fails.